Patients who have a locally advanced or recurrent rectal carcinomas have a poor prognosis. In an effort to make more of the patients candidates for resection of their tumors, preoperative radiation therapy (RT) has been utilized and has become standard practice. However, conventional RT will only convert approximately 50% of these patients into candidates for resection. More recently it has been appreciated that RT plus 5FU enhances survival after successful resection of rectal cancer. The objectives of this study are to: 1) assess the feasibility of administering Hydroxyurea in conjunction with radiation (RT) and 5-fluorouracil (5FU) for locally advanced or recurrent rectal CA; 2) to assess the toxicity of Hydroxyurea when used in conjunction with RT and 5FU in rectal CA; 3) to determine the maximum dose of hydroxyurea tolerate in locally advanced rectal CA patients receiving a standard dose of 5FU and RT; and 4) to evaluate the response of the tumors to chemo-radiotherapy.